UC San Diego Professor and Team Map Air Particles

Jul 01, 2009

Lynn Russell, a professor of atmospheric chemistry at Scripps Institution of Oceanography at UC San Diego, and her team have sampled air from the tip of the
Scripps Pier since last year, creating a near real-time record of what kinds of particles—from sea salt to car exhaust—are floating around at any given time.

Using data on wind speed and direction, the scientists can tell where particles came from and can map their pathways around Southern California.

When Russell and her students put it all together, the atmosphere of greater San Diego comes alive in colors representing the presence of different airborne chemical compounds in aerosol form. One streak of deep red draws a distinct line from the pier that sometimes extends all the way to Las Vegas. The red denotes organic mass, a carbon-based component of vehicular and industrial emissions that pops up on the readouts frequently. Plot the streak on a road atlas and it reveals the daily life of pollution in Southern California. For one stretch of time, it neatly traced Interstate 15 all the way past the California-Nevada border.

"We were really surprised," said Russell. "We did not expect to have such consistent winds for the selected study days."

The hunt for various types of aerosols is helping the research team draw new kinds of global maps, ones that depict what organic compounds—whether natural or from sources such as Southern California traffic and industries—could do to affect rainfall, snowfall, atmospheric warming and cooling, and a host of other climate phenomena. Russell is part of an effort that involves several researchers at Scripps and UCSD and around the world. Collectively they are attempting to address a human-caused phenomenon in the Earth system scarcely considered before the last decade.

Aerosol research is considered one of the most critical frontiers of climate change science, much of which is devoted to the creation of accurate projections of future climate. These projections are generated by computer models—simulations of phenomena such as warming patterns, sea level fluctuations, or drought trends. The raw data for the models can come from historical records of climate basics like temperature and precipitation, but scientists often must rely on incomplete data and best guesses to represent more complex phenomena. The more such uncertainty goes into a model, the greater its margin of error becomes, making it less reliable as a guide for forecasts and adaptive actions.

Among these complex phenomena, the actions of aerosols are what some researchers consider the field's holy grail, representing the biggest barrier to producing accurate representations of climate. In fact, the Intergovernmental Panel on Climate Change in 2007 specifically listed the effect of aerosols on cloud formation as the largest source of uncertainty in present-day climate models.

Russell has taken part in two recent analyses of polar air to understand where its imported aerosols come from and how the chemical components of those aerosols could be affecting temperature and cloud formation. From a research vessel in the Norwegian Sea and via continuous measurements from a ground station in Barrow, Alaska, Russell's team is analyzing particles likely to have been blown to the Arctic from Europe and Asia. Her group has just compiled a full season of air samples fed through intake valves onto filters collected at Barrow.

With it, she believes she has proven what colleagues have previously theorized about where the particles are coming from. She is especially interested in organic particles—aerosols containing carbon supplied either by natural sources such as ocean or land plants or by human sources. Work in her group has shown that organics in the spring haze carry a signature consistent with dust and biomass burning taking place most likely in Siberia. The chemical signature changes in other seasons, revealing itself in infrared spectroscopy readings to be the product of aerosols from natural sources.

"Understanding the big picture is the only way we're going to be able to reduce the uncertainty associated with aerosol particles and their effects on climate," said Russell. "There are so many parameters, there's no one instrument or even one person who can do all of it at once."